Unlocking secrets of water management in cotton

Combined with a much more current series of tests to map the cotton plant genome, the old and the new may combine to unlock some of the secrets of water management in cotton that have challenged cotton farmers for centuries.

Back in the late 1970s, the U.S. was in the midst of an OPEC oil embargo and subsequent gasoline shortages, complete with long lines at the pump and in some cases alternate days in which motorists could buy fuel.

That scenario was the backdrop for a series of U.S. Department of energy-sponsored tests to determine how much residue farmers could take off the soil to use for fuel.

While most studies came and went, generating valuable and useful tillage information, a study at the PeeDee Agriculture Research and Extension Center near Florence, S.C., remains today and sheds some interesting light on the benefits, and lack thereof in some cases, of long-term no-till farming.

Combined with a much more current series of tests to map the cotton plant genome, the old and the new may combine to unlock some of the secrets of water management in cotton that have challenged cotton farmers for centuries.

USDA Agronomist Phil Bauer, who has spent most of his career at the South Carolina facility, showed samples of soil that has been no-tilled since 1978, compared to soil from continuous conventional-tillage for the same period of time.

While the visual results were easy enough to see, Bauer cautioned that these differences didn’t always result in higher crop yields.

Since 1978, researchers at the PeeDee Station have monitored the test fields, which have been in either conservation-tillage or conventional-tillage for over 30 years.

For the first three years of the study, corn was planted each year on the two test sites. From 1982 until 1986, the fields were in a corn, wheat and soybean rotation.

In 1987, there was a severe drought and nothing was planted on the test site and for the next nine years there was a corn, wheat and cotton rotation there, followed by five years of corn, wheat and soybeans.

From 2003 until 2010, researchers switched to corn, rye and soybeans, followed by corn and cotton last year.

In conventional-tillage plots, fields were disked twice, then smoothed with a ‘do-all’ and sub-soiled and planted. Conservation-tillage plots were sub-soiled and planted.

After 30-plus years, samples from the conservation tillage fields showed significant organic matter in the top three inches of the soil — clear enough for growers to plainly see during Bauer’s presentation at the recent field day.

Soil from the conventional-tillage plots was just a clearly devoid of organic matter — exactly what you would expect, Bauer says.

“Corn has been in these tests in most of the years of the project and some years yields were higher in conventional and in other years higher in conservation-tillage plots. Over the first 30 years of the test, he says, overall corn yields were virtually the same.

Soybeans were less frequently in the tests, but were planted off and on throughout the first 30 years of the ongoing project. Again, over all the years of soybeans in the two tillage system, the total yield was very much the same — right around 30 bushels per acre, Bauer adds.

Would expect higher yields

Most growers would likely expect higher yields from conservation-tillage in drought years. With the ground covered and more organic material in the soil, better water usage would be expected. In corn, during the drought years of 1998-2001, conservation-tillage produced a 4 percent yield advantage.

In a soybean and wheat double-crop, it was a different story, Bauer notes. During the same time frame soybeans planted directly into wheat straw in the conservation-tillage plots produced a five percent decrease in soybean yields and three percent decrease in wheat yields.

“During that same time period and on a different area of the research farm, I had a test comparing the effects of no-till versus conventional-tillage on the exact same kind of soil on cotton, and we saw a 22 percent yield increase on the no-till plots,” Bauer notes.

Cotton is grown in 30 countries around the world, under sometimes dramatically different climatic conditions and on many different soil types. The one common denominator in yield and quality of cotton grown anywhere in the world is water.

USDA researchers recently documented the genes that help regulate water flow through a cotton plant. This study combined with the long-term tillage study, dating back to 1978 offer a near perfect environment to study how to best manage the water carrying capabilities of cotton.

A major facilitator of water movement through cell membranes of cotton and other plants are the aquaporin proteins. Aquaporin proteins are present as diverse forms in plants, where they function as transport systems for water and other small molecules.

“We now know, based on results of these recent tests, that there are 71 genes in cotton that regulate how water moves through the cells of a cotton plant. And, we know that certain microbes in the soil can turn on the genes in the cells that help regulate water in the cotton plant,” Bauer says.

The USDA study presents a comprehensive identification of 71 cotton aquaporin genes. Phylogenetic analysis of amino acid sequences divided the large and highly similar multi-gene family into the known 5 aquaporin subfamilies.

Lead researcher on the project and USDA-ARS scientist Wonkeun Park says, “Together with expression and bioinformatic analyses, our results support the idea that the genes identified in this study represent an important genetic resource providing potential targets to modify the water use properties of cotton.

“The significance of the multi-gene family of aquaporin transmembrane proteins is emerging from studies aimed at optimizing water and nutrient use efficiency.

“This large gene family has been shown to be highly diversified in plants and thus likely harbors functionally multifaceted behaviors in plants under various growth circumstances.

“Since the global importance of cotton as a primary natural fiber source in production agriculture is well established, our goal in this study was to identify all the members of the aquaporin family in the cotton genome,” he says.

Bauer adds that over the next few years, researchers at the PeeDee Station will look at cotton in comparison to corn to determine the different amounts of these microbes that occur in conventional versus long-term tillage.

“We want to know better ways to manage the soils in the two different crops,” the USDA researcher says.